Tag Archives: thermowell

Fermentasaurus Thermowell and pressure ferments

I brew in a fermentation fridge and use a BrewPi to control the fermentation temperature. To get the most accurate control of beer temperature, I’ve been using stainless thermowells in my plastic fermenters. I was excited about the Fermentasaurus product (in particular the pressure fermenting capability), but noticed that it had no allowance for a thermowell. I reached out to the manufacturer and they came back with the following ideas:

  1. Strap the temperature probe to the outside of the vessel (their recommended method)
  2. Add another hole + grommet to the lid and use a thermowell (not recommended – but will work).

I questioned whether the second option would still allow me to ferment under pressure, and they came back saying that the pressure on the hole should be quite low and a grommet should be able to hold it. They highlighted that it was at my own risk though and that I should do a pressure test after fitting it.

So I pulled the trigger and drilled a hole in my lid next to the Gas post. A few notes here:

  • I used a 13mm spade bit as the plastic of the lid is quite thick. The challenge is holding the lid still whilst you drill. I cleaned up the hole using a plastic reamer.
  • I already had a 40CM stainless (9mm diameter) thermowell with a rounded bottom end (the pinched thermowells I’ve found tend to tear the grommets when you push them through). I got my 40cm thermowell from Beerbelly.
  • The grommet I used was bigger (20mm OD/9mm ID) than a normal lid grommet (and thicker). I got it from Sydney Home Brew Supplies on eBay in a 10 pack. It was slightly tricky to get it into the hole, but once it was through, it sits very neatly (and tightly) around the thermowell, especially when mounted in the lid.
Large grommet size (20mm) with small one (15mm) and thrown for comparison + the thermowell

I pressure tested and have used for 5 brews since May 2017 with no leaks or loss of pressure. I’ve used for both normal (airlock) and pressure ferments.

The final results can be seen here:

Top view of the installed thermowell

Side view of the installed thermowell